The present invention generally relates to heat shields, and more particularly, to a lightweight, oxidation resistant insulating sandwich tile for use in spacecraft heat shields and the like.
Thermal control of spacecraft surfaces during planetary entry and earth reentry is an important technology that enables accomplishment of the intended mission of the spacecraft (e.g., science gathering, routine access to space, etc.). Previously, protective heat shields have incorporated ablators for the rejection of aerothermal heat loads through the pyrolysis and ablation of the ablative material comprising the ablator.
Traditional protective heat shields have generally consisted of ablatable materials that are impregnated into a honeycomb core structure (for spacecraft), rigid ceramic tiles, or ceramic fibrous tiles. Unfortunately, fabrication of these types of heat shield materials, particularly phenolic impregnated carbon ablator (PICA), has typically not been as re- producible and reliable as desired. Further, rigid ceramic tiles can be relatively expensive to fabricate and suffer from relatively poor toughness and thermal shock resistance. While ceramic fibrous tiles do provide improved toughness and thermal shock resistance over rigid ceramic tiles, they are very expensive to fabricate and can require very long lead times.
In view of the foregoing, one objective of the present invention is to provide a lightweight, less fabrication sensitive modular thermal protection system (TPS) for use in thermal protection applications such as, for example, spacecraft heat shields.
These and other objectives and advantages are achieved by the inventive materials concept for a lightweight insulating sandwich tile in accordance with the present invention. According to one aspect of the present invention, a lightweight insulating sandwich tile includes a structural facesheet comprised of an ablative first material. An inner insulating core comprised of a second material having low density and low thermal conductivity is attached to an inner surface of the structural facesheet. The lightweight insulating sandwich tile also includes an oxidation resistant outer layer on an outer surface of the structural facesheet. In one embodiment, the oxidation resistant outer layer may comprise a coating applied on the outer surface of the structural facesheet.
The ablative first material may comprise carbon-carbon. In this regard, the carbon-carbon ablative first material may be laid-up in a single ply configuration, or it may be laid-up in a quasi-isotropic configuration. The second material may, for example, comprise bonded discontinuous carbon fibers (e.g., carbon FIBERFORM(copyright) commercially available from Fiber Materials, Inc., of Biddeford, Me. or CALCARB(trademark) commercially available from Calcarb, Inc., in Rancocos, N.J.), carbon foam (a network of vitreous carbon ligaments), carbon aerogel or graphite felt. The oxidation resistant outer layer may comprise a coating or surface treatment of, for example, MoSi2, amorphous SiCN, amorphous SiCBN, Ti3SiC2, HfC, HfO2, HfB2, SiC, Ir, or ZrB2, that is applied on the outer surface of the structural facesheet.
The structural facesheet and the inner insulating core may be attached to one another. In this regard, the structural facesheet and the inner insulating core may be bonded to one another by disposing at least one layer of one of a phenolic loaded scrim cloth or a phenolic loaded felt there between and applying heat to remove phenolic volatiles. The structural facesheet and the inner insulating core may also be attached to one another by co-curing the structural facesheet and the inner insulating core.
To enhance the structural integrity of the lightweight insulating sandwich tile, the inner insulating core may include a plurality of support panels. The support panels may, for example, be comprised of carbon-carbon, bonded discontinuous carbon fibers, and/or a network of vitreous carbon ligaments. Each of the support panels may be oriented in a parallel fashion to one another and substantially orthogonal to the structural facesheet. Sections of lightweight insulating material (e.g., carbon aerogel and/or graphite felt) may be disposed between each of the parallel support panels.
According to another aspect of the present invention, a lightweight insulating sandwich tile includes an outer structural facesheet and an inner insulating core backing the outer structural facesheet. The outer structural facesheet and the inner insulating core may be attached to one another by, for example, disposing at least one layer of one of a phenolic loaded carbon scrim cloth or a phenolic loaded carbon felt there between and applying heat to remove the phenolic volatiles or co-curing the outer structural facesheet and the inner insulating core. The outer structural facesheet is comprised of carbon- carbon (e.g., in a single ply lay-up or a quasi-isotropic lay-up) and includes an oxidation resistant coating or surface treatment on an outer surface thereof. In this regard, the oxidation resistant coating or surface treatment may, for example, comprise MoSi2, amorphous SiCN, amorphous SiCBN, Ti3SiC2, HfC, HfO2, HfB2, SiC, Ir, or ZrB2,. The inner insulating core backing the outer structural facesheet is comprised of bonded discontinuous carbon fibers, a network of vitreous carbon ligaments, carbon aerogel, and/or graphite felt. The structural integrity of the lightweight insulating sandwich tile may be enhanced by including a plurality of support panels comprised of, for example, carbon-carbon, bonded discontinuous carbon fibers, and/or a network of vitreous carbon ligaments in the inner insulating core. The support panels may be parallel to one another and substantially orthogonal to the outer structural facesheet with sections of lightweight insulating material (e.g., carbon aerogel and/or graphite felt) disposed between each of the parallel support panels.